Latest results from PHOBOS at RHIC

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Latest results from PHOBOS at RHIC
Gábor Veres for the
collaboration Eötvös Loránd University, Budapest
La Thuile, Aosta Valley, Italy, March 12-19, 2005
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Collaboration (March 2005)
Burak Alver, Birger Back, Mark Baker, Maarten
Ballintijn, Donald Barton, Russell Betts, Richard
Bindel, Wit Busza (Spokesperson), Zhengwei Chai,
Vasundhara Chetluru, Edmundo García, Tomasz
Gburek, Kristjan Gulbrandsen, Clive Halliwell,
Joshua Hamblen, Ian Harnarine, Conor Henderson,
David Hofman, Richard Hollis, Roman Holynski,
Burt Holzman, Aneta Iordanova, Jay Kane, Piotr
Kulinich, Chia Ming Kuo, Wei Li, Willis Lin,
Steven Manly, Alice Mignerey, Gerrit van
Nieuwenhuizen, Rachid Nouicer, Andrzej Olszewski,
Robert Pak, Corey Reed, Eric Richardson,
Christof Roland, Gunther Roland, Joe Sagerer,
Iouri Sedykh, Chadd Smith, Maciej Stankiewicz,
Peter Steinberg, George Stephans, Andrei
Sukhanov, Artur Szostak, Marguerite Belt Tonjes,
Adam Trzupek, Sergei Vaurynovich, Robin Verdier,
Gábor Veres, Peter Walters, Edward Wenger,
Donald Willhelm, Frank Wolfs, Barbara Wosiek,
Krzysztof Wozniak, Shaun Wyngaardt, Bolek
Wyslouch ARGONNE NATIONAL LABORATORY BROOKHAVEN
NATIONAL LABORATORY INSTITUTE OF NUCLEAR PHYSICS
PAN, KRAKOW MASSACHUSETTS INSTITUTE OF
TECHNOLOGY NATIONAL CENTRAL UNIVERSITY,
TAIWAN UNIVERSITY OF ILLINOIS AT
CHICAGO UNIVERSITY OF MARYLAND UNIVERSITY OF
ROCHESTER
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The PHOBOS detector (2004)
NIM A499, 603-23 (2003)
T0 counter
TOF
SpecTrig
Paddle Trigger counter
calorimeter
Magnet
Paddle Trigger counter
Spectrometer
T0 counter
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PHOBOS White Paper
nucl-ex/0410022

• Lot of excitement, theoretical workshop at BNL
  in 2004
• experimental White Papers
  about discoveries
• Summarizes the most important results from
  PHOBOS
• in the last years
• Emphasis on simple scaling features of the data,
  which
• have important physics implications, and give
  predictions

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Some exciting topics in the field
we will discuss

• Suppression of high-pT particles, jet quenching
• Initial energy density, multiplicities,
  boost-invariance?
• Collective effects, collective flow of
  particles, equation of state

These are relevant for studying the new type of
matter created in heavy ion collisions!
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I. pT-spectra
AuAu 62.4 GeV
How do the spectra scale with centrality?
And with collision energy?
(How does one quantify centrality?)
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Centrality measures
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Centrality measures
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RAA at 200 and 62.4 GeV (AuAu)
pp reference data 62.4 GeV ISR SFM,
0.5lt?lt1 200 GeV UA1 -2.5lt?lt2.5 (acceptance
correction with PYTHIA)
Gradual suppression compared to Ncoll scaling.
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RAA
Npart
PERIPHERAL
CENTRAL
Yields normalized by Npart are less
centrality-dependent
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Factorization energy, centrality
PRL 94, 082304 (2005)
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How does all this depend on system size (ion mass
number)?
Centrality and A can be dialed separately
AuAu, peripheral
CuCu, central
similar Npart, different geometry
Half a BILLION CuCu events recorded recently
for this analysis (at 200 GeV)!
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II. Multiplicity (dN/dh)
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Extended longitudinal scalingAuAu
Also observed earlier in pp
PRL 91, 052303 (2003)
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Simple dN/dh prediction for LHC
Acta Phys. Polon. B35, 2873-94 (2004)
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dAu
pEm
Heavy Ion Rest Frame
p or d rest frame
dAu
pPb
nucl-ex/0403033
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No Plateau in Rapidity Distributions
Plateau in Pseudorapidity Distributions is
Misleading Rapidity Distributions of Pions are
Gaussian
PRL 91, 052303 (2003) nucl-ex/0403050
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III. Elliptic Flow (v2)
Initial spatial anisotropy
z
z
Reaction plane (YR)
y
f
x
y
y
x
x (defines YR)
dN/d(f -YR ) N0 (1 2v1cos (f-YR)
2v2cos (2(f-YR)) ... )
Final momentum anisotropy
py
px
Secondary interactions, collective effect!
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Longitudinal scaling in v2
v2 as a function of hh-ybeam
Accepted by PRL, nucl-ex/0406021
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Summary transverse and longitudinal scaling

• pT spectra of hadrons are suppressed relative to
  Ncoll scaling, but approximately scale with
  Npart.
• The energy and centrality dependence of pT
  spectra factorize.

• Originally expected boost-invariance in
  mid-rapidity region was not observed.
• Scaling in extended h region seen in AuAu, dAu
  and (previously) in pp and pA,

both in dN/dh and v2.
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BACK-UP SLIDES
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Centrality Determination
AuAu
DataMC
200 GeV
b (fm)
Npart
Paddle signal (a.u.)
62.4 GeV
Paddle signal (a.u.)
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pp(p) reference at 62.4 and 200 GeV
Z Phys. C 69, 55 (1995)
Nucl. Phys. B 207, 1 (1982)
Phys. Lett. B 83, 257 (1979)
Nucl. Phys. B 335, 261 (1990)
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Cronin Effect in dAu vs. Centrality
6 most central AuAu
Phys.Rev.Lett. 91, 072302 (2003)
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Identified mT-spectra at 200 GeV
AuAu
200 GeV
Spectra normalized at 2 GeV/c
dAu
p
Phys.Rev. C 70, 051901 (2004)
Scale uncertainty 15
Not feed-down corrected
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High statistics dAu track sample
p
p
K
positives, 1.6ltplt1.8 GeV/c
p
p
K
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Upgrades in PHOBOS for the dAu run (2003)
TOF
TOF
mini-pCal
dAu, pp
T0
Response to Importance of High PT Studies
SPECTRIG
T0
pCal

• Moved TOF walls far (5 m) from IP
• New, on-line high pT Spectrometer Trigger
• New start-time (T0) Cerenkov detectors
• On-line vertexing and ToF start time
• Forward proton calorimeters on Au and d sides
• DAQ upgrade (x10 higher rate!)

AuAu
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Trigger detectors (dAu)
Segmented scintillator detectors at 45 and 90
degrees from beam line
Combined with the ToF walls
ToF
accepted
rejected
SpecTrig

• selects events with particle
• hitting ToF and SpecTrig walls
• enhances high-pT (straight)
• tracks online tracking
• decision-making in 50 ns